How to toggle selectable of multiple objects?
OK, you've already added 'Selectable' to your visible restriction toggles in the outliner.

Create a new collection for the objects you want to make simultaneously selectable / non-selectable. Call it, say, 'S1'.
Select the objects of interest in the 3D view or the outliner, and ShiftM link them to 'S1'. (It's a link, not a move, it won't screw up your existing organisation.)
When you want to toggle the selectability of all the items linked in S1, Shift-click the dart icon next to the 'S1' folder.